2 H 2 + O 2 → 2 H 2 O

2 H2 + O2 → 2 H2O

+

• Identify the factors that could affect the rate of a chemical reaction.

• Use the Collision Theory to explain the factors influencing the rate of a reaction.

• Explain the effect these factors have on the shape of a kinetic energy distribution curve.

Factors Affecting Reaction Rates

• presence/absence of a catalyst.

• surface area (particle size)

• concentration or pressure of a reactant

• temperature

• nature of the reactants

Effect of Particle Size (surface area)

Rate of reaction increases with increased surface area (crushing, grinding) .

More particles involved, more frequent collisions.

Effect of Concentration

Rate of reaction increases with increased concentration (mol/L) of particles.

More particles with activation energy - more chances of a successful collision.

Effect of PressureOnly affects reaction rates of gaseous reactions.

Rate of reaction increases with decreased volume of the container - mimics higher [ ].

Closer particles – more chance of collisions.

Effects of a Temperature ChangeRate of reaction increases with increased temperature.

More KE per particles – more frequent collisions and more EA.

10°C increase in temp usually doubles reaction rate.

Effect of the Nature of Reactants

1. Comparing reactions with similar compounds:

Less bonds to break, faster the reaction.

2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)

2 NO(g) + O2(g) → 2 NO2(g)

Covalent bonds takes longer to break than aqueous.

(aq) are already separated into ions, so are instantaneous.

KNO3(aq) + NaI(aq) → KI(aq) + 2 NaNO3(aq)

2. Comparing reactions with similar bond numbers:

H2(g) + I2(g) → 2 HI(g)

KNO3(aq) + NaI(aq)→ KI(aq) + NaNO3(aq)

K+

Na+

I-

NO3-

3. Comparing similar compounds and similar bond numbers:

(g) faster > (l) > (s)

• Stronger IMF to overcome• Less KE per particle• Less collisions • Less Surface area

Effect of Catalysts

A catalyst speeds up or starts a reaction by lowering the activation energy.

An inhibitor is the opposite of a catalyst.

Enzymes are known as biological catalysts.

• Does not alter products or ΔH.• Not involved in the overall chemical reaction• Appears unchanged.

Things that increase reaction rate:

· increased surface area· increased concentration· increased pressure· increased temperature· fewer bonds, aqueous or gas states· catalyst

To decrease reaction rate - do the opposite....